1. Field of the Invention
The present invention relates to an electrical contact for relay suitable for, for example, vehicle-mounted relay or the like and a method for manufacturing the same.
2. Description of the Related Art
In general, a vehicle-mounted electromagnetic relay used in a motor load circuit or the like has a structure in which a pair of fixed contacts, i.e., a normal-open side (hereinafter referred to as “NO-side”) fixed contact and a normal-close side (hereinafter referred to as “NC-side”) fixed contact is arranged so as to sandwich a movable contact, and has a function of switching two electrical circuits by alternately contacting a movable contact with two fixed contacts.
For example, for an electromagnetic relay for switching ON/OFF of a wiper driving motor, wearing resistance characteristics and welding resistance characteristics for a motor drive current which is a large load current are required for the NO-side contact pair, and characteristics for suppressing a material transition projection to be formed by a motor braking circuit are required for the NC-side contact pair. The direction of the rotation of a motor is switched using electromagnetic relays in pairs so as to open/close a power window. Also in this case, wearing resistance characteristics and welding resistance characteristics are required for the NO-side contact pair, and characteristics for suppressing the formation of a material transition projection are required for the NC-side contact pair.
In particular, in a hinge-type electromagnetic relay for general purpose, the contact force at the contact of the NC-side contact pair cannot be principally increased as compared with that of the NO-side contact pair, and thus, the contact chattering occurs at the NC-side contact pair many number of times for a long time. Consequently, the amount of contact transition caused by a short-arc generated during the contact chattering increases, and thus, a contact locking occurs due to transition projections and holes generated in the NC-side contact pair, which may cause malfunction of the electromagnetic relay. In order to solve the problems, the contact hardness of the NC-side contact pair needs to be made lower than that of the NO-side contact pair.
As described in these examples, since the characteristics required for the NO-side contact pair are different from that required for the NC-side contact pair in the application of an electromagnetic relay often used in vehicles, it is preferable that a contact material suitable for each of the contact pairs be selected.
For this reason, conventionally, Patent Document 1 discloses a method for manufacturing a rivet-shaped clad electrical contact in which a silver-cadmium type unoxidized material or a silver-tin type unoxidized material and a silver or a silver-3-15% by weight of nickel alloy are cold welded and molded into a rivet shape, and the resulting material is then subjected to oxidization by heating in a pressurized oxygen atmosphere of 3 atm or higher at a temperature of 600° C. to 850° C. to thereby oxidize the silver-cadmium type unoxidized material or the silver-tin type unoxidized material to the silver-cadmium oxide type oxidized material or the silver-tin oxide type oxidized material.
In this technology, an electrical contact manufactured as described above is attached to a transfer type electrical contactor. By doing so, even when such electrical contact is used under the condition that large amount of current flows through one of the contact pairs and small amount of current flows through the other one, welding and wearing of a large-amount-of-current-side contact pair are suppressed, and contact resistance of a small-amount-of-current-side contact pair is small so as to ensure stable contact and conduction.